This invention relates to grinding aids for cement clinker, and to the use of certain direct process residue gels as grinding aids for pulverizing cement clinker to cement. In particular, the grinding aids are hydrolysis products of alkylhalodisilanes and other chlorosilanes produced in alkylhalosilane manufacturing operations.
The grinding aids are capable of reducing the energy consumption in the cement clinker grinding operation. For example, when the compositions are used in cement clinker grinding, one can reasonably expect about a thirty percent increase in surface area of the cement by the addition of about 1,000 ppm of the grinding aid composition during each batch grinding operation. Also, concrete made from such cements exhibits about a five percent increase in standardized 28-day compressive strength comparisons.
These grinding aid compositions based on hydrolyzed products of methylchlorodisilanes offer significant cost advantages over conventional types of grinding aids, such as triethanolamine and diethylene glycol.
The cement produced in the greatest volume and the one most widely used in concrete for construction is Portland cement. Portland cement is a hydraulic cement, i.e., it sets, hardens, and does not disintegrate in water. The term cement, therefore, as used herein is intended to define inorganic hydraulic cements, principally Portland and related cements. The essential feature of such cements is their ability on hydration to form with water relatively insoluble bonded aggregations of considerable strength and dimensional stability.
Hydraulic cements are manufactured by (i) processing and proportioning a number of raw materials, (ii) burning the raw materials, i.e., clinkering them at a suitable temperature, and (iii) grinding the resulting hard nodules called clinker to a fineness required for an adequate rate of hardening by reaction with water.
Most Portland cements consist mainly of tricalcium silicate Ca3SiO5 and dicalcium silicate Ca2SiO4. Typically, and in this regard, two types of raw materials are required, (a) one being rich in calcium such as limestone, chalk, marl (cement rock), oyster shells, or clam shells; and (b) the other being rich in silica such as clay or shale. The two other most significant phases in any Portland cement are tricalcium aluminate Ca3Al2O6 and a ferrite phase. A small amount of calcium sufate CaSO4 in the form of gypsum or anhydrite is also added during grinding to control the setting time and to enhance the strength development.
Clinker in Portland cements manufactured from raw materials including components such as calcium carbonate, clay, shale, or sand, is formed by passing such raw materials through a kiln at increasing temperatures during their passage through the kiln. In the kiln itself, free water is evaporated, any water combined with clay is released, magnesium carbonate is decomposed, calcium carbonate is decomposed (calcination), and the lime and clay oxides are combined.
Thus, the process of Portland cement manufacturing consists of (i) quarrying and crushing the rock, (ii) grinding carefully proportioned materials to a high fineness, (iii) subjecting a raw mix to pyroprocessing in a rotary kiln, and (iv) grinding the resulting clinker to a fine powder. Typically, the rock or stone is crushed; the various raw materials are then ground to a powder and blended; the raw mix is converted (changed chemically) into cement clinker by burning the raw mix; and the clinker and gypsum are ground into Portland cement and shipped. These hydraulic cements function as intermediate products used for making concrete, mortar, grout, and composite materials such as asbestos-cement products.
It is not unusual for industrial by-products to be used as raw materials for cement, including such by-products as slags containing carbonate-free lime, silica, and alumina; and fly ash from utility boilers containing finely dispersed silica and alumina.
As an example, U.S. Pat. No. 5,374,310 (Dec. 20, 1994) is directed to the addition of certain direct process residue gels to a cement kiln upstream of the grinding operation, to provide part or all of the silica source for the cement by calcining. In contrast, and according to the present invention, however, the direct process residue gels are added directly to the grinding operation in limited amounts, and without calcining, in order to improve the grinding efficiency. Thus, the present invention differs from the ""310 patent in the point of addition of the gel, the gel""s function, and the purpose of the gel.
This invention is directed to a process for manufacturing hydraulic cement in which (i) raw materials are crushed and ground, (ii) the crushed and ground raw materials and other components are burned and calcined to prepare a cement clinker, and (iii) the cement clinker is ground to a fine powder. The improvement contributed according to the present invention is that a certain grinding aid is added to the cement clinker before it is ground in (iii). The grinding aid is an uncalcined direct process residue gel, which is an hydrolysis product of alkylhalodisilanes produced as by-products in the manufacture of alkylhalosilanes.
Preferred grinding aids are high boiling residues of the direct process which have been neutralized to form gels. Typically, these gels are aqueous compositions containing from 1 to about 55 percent by weight of solids, and the balance of the composition to 100 percent is water. The solids typically comprise about 1 to about 50 percent by weight of silicon fines, about 1 to about 40 percent by weight of metal salts, and the balance of the solids to 100 percent by weight is the hydrolysis condensation products of mixed alkylhalosilanes and alkylchlorodisilanes.
These and other features of the invention will become apparent from a consideration of the detailed description.
Silicon containing compositions useful in this invention, i.e., the direct process residue gels, are described in U.S. Pat. No. 4,408,030 (Oct. 4, 1983), incorporated herein by reference. This invention herein provides a viable avenue for the recovery of value from such chlorosilicon containing by-products as they are generated during commercial production of silicone polymers. These compositions can be obtained from, for example, processes for reacting silicon metalloid with hydrogen chloride to form chlorosilanes. Thus, chlorosilicon by-products can be obtained from what is commonly called the direct process, where an organochloride such as methyl chloride is reacted with silicon metalloid to form organochlorosilanes. These chlorosilicon by-products typically contain distillation residues, off-specification materials, and excess chlorosilanes.
Thus, according to the direct process, silicones are prepared from silica by reducing silica in an electric furnace to elemental silicon:
SiO2+2 Cxe2x86x92Si+2 CO.
The elemental silicon is then treated with compounds such as RCl, typically methyl chloride, according to the direct process:
Si+2RClxe2x86x92R2SiCl2.
While other products are also obtained, the main product is R2SiCl2.
Hydrolysis of the main product R2SiCl2 organochlorosilanes, typically Me2SiCl2, provides siloxane structures which are used in the manufacture of a variety of other silicone products:
(n+m) Me2SiCl2+2(n+m) H2Oxe2x86x92(Me2SiO)m+2(n+m) HCl+HO(Me2SiO)nH.
Chlorosilicon by-products and processes for hydrolyzing the compositions to direct process residue gels which are useful according to this invention can be prepared by preferred processes in which the chlorosilicon by-product has an SiCl functionality of the material to be hydrolyzed greater than or equal to about 2.8. The average SiCl functionality of the material to be hydrolyzed can be maintained within the prescribed limit by determining the average SiCl functionality of the chlorosilicon by-product and blending it with other chlorosilicon by-products to arrive at the desired average SiCl functionality.
As used herein, the term SiCl functionality of a given chlorosilicon by-product is intended to mean the number of Sixe2x80x94Cl bonds in the chlorosilicon compound. Some representative compounds and their SiCl functionality f are R3SiCl with f=1, R2SiCl2 with f=2, RSiCl3 with f=3, SiCl4 with f=4, RCl2SiSiCl2R with f=4, RCl2SiSiCl3 with f=5, and Cl3SiSiCl3 with f=6, where R represents a non-chlorine organic radical. The average SiCl functionality of the chlorosilicon by-product is therefore the weighted average of SiCl functionality of all Sixe2x80x94Cl containing compounds in the by-product.
Chlorosilicon compounds that may be present within the chlorosilicon by-product include organic substituted and non-organic substituted silanes, disilanes, disiloxanes, silane oligomers, siloxane oligomers, silphenylenes, and silalkylenes, in which at least one Sixe2x80x94Cl bond is present. In addition, it may contain silicon metal fines, metallic copper fines, metal salts, and silicon containing compounds without any Sixe2x80x94Cl bonds.
In preparing the composition, the chlorosilicon by-product with the appropriate average SiCl functionality is added to an aqueous medium which is agitated to facilitate hydrolysis. Both the rate of addition of the chlorosilicon by-product(s) to the aqueous medium, and the rate of agitation of the resulting mixture, can be used to control the particle size of the resulting particulate silicon containing product, i.e., the direct process residue gel. The aqueous medium may consist of only water initially, in which case hydrogen chloride formed by the hydrolysis dissolves in the water. The aqueous medium may also initially contain hydrogen chloride. The term aqueous is intended to mean that the medium contains essentially water as the component reacting with the chlorosilicon by-product, and excludes such organic components as alcohols which are reactive with the chlorosilicon by-product. Thus, the aqueous medium may be in the form of a slurry containing greater than zero to about 20 percent CaO. The amount of the aqueous medium being used can be varied provided sufficient water is employed to completely hydrolyze the chlorosilicon by-product.
Typically, hydrolysis is conducted at temperatures between 20xc2x0 C. and the boiling point of the aqueous medium. It is preferred that the hydrolysis be carried out at temperatures in the range of about 60 to 105xc2x0 C. As hydrolysis progresses, a particulate silicon containing product separates from the aqueous medium, i.e., the direct process residue gel. The silicon-containing product may be removed from the aqueous medium by filtration, phase separation, or centrifugation. The resulting solid silicon containing product is washed with water one or more times to reduce its chloride content.
One particularly preferred cement clinker grinding aid composition according to the present invention is best characterized as being a high boiling residue from the direct process. This high boiling residue is neutralized with lime slurry (CaO+water) and produces a gel in the form of a water containing composition of 1 to about 45 percent by weight of a crosslinked polysiloxane. The gel according to this invention is referred to by reference to the acronym DPR Gel, i.e., direct process residue gel.
The composition used in the following examples contained 1 to about 55 percent by weight of solids, and the balance of the composition to 100 percent was water. As noted above, the solids consisted of about 1 to about 50 percent by weight of silicon fines, about 1 to about 40 percent by weight of metal salts, and the balance of the solids to 100 percent by weight were hydrolysis condensation products of mixed alkylhalosilanes and alkylchlorodisilanes.
When used as a grinding aid, the DPR gel can be added as-produced, or it may be slurried and pumped to the grinding process using a suitable slurrying medium such as water. The concentration of the grinding aid, will for economic effectiveness, depend on the material being milled, and the concentration level can be easily determined by one skilled in the art. For example, when used for grinding clinker, the DPR gel functions to reduce the grinding energy required to achieve a desired particle size, and so the most effective DPR gel levels of concentration can be in the range of about 200-10,000 ppm, particularly a range of about 800-1,200 ppm.